That particular PSU was first released back in 2007 and was discontinued years ago, how old is the one that you have.
It the PSU is so old that it is out of warranty I would not use it anywhere near my computer and especially if it had a video card that cost circa 6500 Krona/$800+.
The card being in the slot but not identified in the specifications could be down to having no drivers** but it could also be hardware related such as not being enabled in the BIOS, the PSU not being up to the task or a bad PCI-E slot on the MB>
windows 10 was installed by a friend
The following not intended as lecture but to hopefully help keep you understand the implications of using unlicensed software.
Your friend should take what they install on other folks computers, fine if they wish to use such software on their computer but using it on yours puts you on the wrong side of the law, the Enterprise version of Windows is used by large capacity users such as the IT industry, hospitals and schools etc, these type of users have what is known as a Volume Licence Key for which they pay an agreed amount with Microsoft, the same Windows product is installed on as many in house computers as is permitted, using the product key on any personal computer is not permitted and is in fact illegal.
** one of the affects of having unauthorised software on your computer will be that at some point you will be blocked from installing any Windows updates, you may already be having an issue with this as Windows would normally download what it deemed the most appropriate Nvidea drivers for your GTX 1080 for you, the fact that it hasn`t may or may not be related to the version of Windows that is installed on your computer.
Microsoft Volume Licensing
- The posting of links or references to warez or any other type of illegal software is strictly forbidden. By doing so you risk having your user account terminated without warning. We will NOT help anyone we suspect of having obtained their software or services illegally.